Last Modified: Sunday, December 30, 2012 at 1:09 a.m.

Ice hangs from citrus as temperatures dipped into the low 20s during a freeze two years ago in Lakeland. Because of the premature fruit drop already, there's concern about a freeze that will affect citrus trees and growers across Florida.

SCOTT WHEELER | THE LEDGER (2010)

The recent cold snap affecting most of the U.S. doesn't give cause for optimism, according to Cliff Harris, a partner in Harris-Mann Climatology of Coeur d'Alene, Idaho, a private consulting firm that tracks the possibilities for Florida citrus freezes.

"There's no way to tell for sure, but the first piece of the puzzle is in place. The bigger piece is coming next month," Harris told The Ledger on Thursday.

Harris discussed his company's Dec. 19 forecast indicating a stronger chance of sub-freezing temperatures hitting Central and South Florida in the middle of January.

It got the attention of the state's citrus growers. Florida Citrus Mutual in Lakeland, the state's largest growers' representative, sent news of the forecast in its daily briefing to membership, said Mark Wheeler, a Lake Placid-based grower and Citrus Mutual president.

"With the high (premature) fruit drop already, there's a heightened concern about a freeze, especially with citrus greening or any other disease or stress on the tree," Wheeler said. "I think everybody wonders what the impact of a freeze would be."

Harris-Mann based its forecast on a climate pattern popularly known as el Niņo (the Christ child), which affects global weather. An el Niņo period sees above-average ocean temperatures and pressure in the equatorial South Pacific Ocean, while the opposite occurs during a la Niņa period.

Historically the chances for a Florida citrus freeze increase during a neutral period, nicknamed la Nada, Harris said. We're in a neutral period now.

A la Nada freeze in Florida occurs when a high pressure ridge stationed over the northwestern U.S. acts like a roller coaster, sending westward winds up into Alaska and the Arctic region, picking up cold weather and sending it plunging southward, Harris said. He compared the effect to a skier picking up speed on a ski jump — the greater the speed one picks up, the farther the skier goes after leaving the jump.

The high pressure ridges usually occur two or more times during a la Nada period, he said. The first one came right on schedule this month, sending cold weather into the south-central U.S., including North Florida. It gave Little Rock, Ark., its first white Christmas since 1926.

But the second high pressure ridge, if it develops, tends to send cold weather even farther south — as much as 400 miles, Harris said. The only question is whether the next roller coaster points to Florida or farther west.

Harris put the odds of a citrus freeze reaching deeper into South Florida, including Polk County, at 40 percent. A citrus freeze occurs when temperatures reach 28 degrees or lower for at least four hours.

Florida has seen many minor freezes in the past two decades, but the last major freeze occurred on Christmas 1989 following other major freezes around Christmas 1983 and January 1985.

Some Wheeler Farms groves in Polk lost 80 percent of their trees during the 1989 freeze, Wheeler said.

Another variable hard to predict is whether temperatures will fall to 28 or lower for the required four hours, Harris said. Central Florida saw freezing weather for the first 14 days in January 2010, devastating tropical fish and tomato growers, but it mostly hovered above citrus freeze conditions.

Citrus growers may not be so lucky next month because temperatures in the far Northern Hemisphere have set record lows this winter, he said.

But even a mild freeze could cause major damage because of citrus greening, a fatal bacterial disease that weakens the tree. Scientists estimate the disease has infected more than half the state's citrus trees.

Florida growers are seeing record rates of premature fruit drop in the 2012-13 crop, which they attribute to the effects of greening.

Marty McKenna, a Lake Wales-based grower and chairman of the Florida Citrus Commission based in Bartow, said he doesn't sense any heightened concern among growers about a stronger chance of a freeze this season.

"If you make a statement there could be colder-than-normal temperatures in the middle of January, you'd be right most years," he said.

But McKenna did not play down the growers' concerns about the impact of a citrus on their already greening-stressed trees.

"With the introduction of greening, we've seen things we've never seen before," he said. "Who can say what will happen with this much greening? A freeze normally picks on weaker trees."

[ Kevin Bouffard can be reached at kevin.bouffard@theledger.com or at 863-401-6980. Read more on Florida citrus on his Facebook page, Florida Citrus Witness, http://bit.ly/baxWuU. ]

<p>Florida citrus growers are watching, preparing and hoping that "la Nada," Spanish for "the nothing," won't leave nada fruit on their trees in its wake.</p><p>The recent cold snap affecting most of the U.S. doesn't give cause for optimism, according to Cliff Harris, a partner in Harris-Mann Climatology of Coeur d'Alene, Idaho, a private consulting firm that tracks the possibilities for Florida citrus freezes.</p><p>"There's no way to tell for sure, but the first piece of the puzzle is in place. The bigger piece is coming next month," Harris told The Ledger on Thursday.</p><p>Harris discussed his company's Dec. 19 forecast indicating a stronger chance of sub-freezing temperatures hitting Central and South Florida in the middle of January.</p><p>It got the attention of the state's citrus growers. Florida Citrus Mutual in Lakeland, the state's largest growers' representative, sent news of the forecast in its daily briefing to membership, said Mark Wheeler, a Lake Placid-based grower and Citrus Mutual president.</p><p>"With the high (premature) fruit drop already, there's a heightened concern about a freeze, especially with citrus greening or any other disease or stress on the tree," Wheeler said. "I think everybody wonders what the impact of a freeze would be."</p><p>Harris-Mann based its forecast on a climate pattern popularly known as el Niņo (the Christ child), which affects global weather. An el Niņo period sees above-average ocean temperatures and pressure in the equatorial South Pacific Ocean, while the opposite occurs during a la Niņa period.</p><p>Historically the chances for a Florida citrus freeze increase during a neutral period, nicknamed la Nada, Harris said. We're in a neutral period now.</p><p>A la Nada freeze in Florida occurs when a high pressure ridge stationed over the northwestern U.S. acts like a roller coaster, sending westward winds up into Alaska and the Arctic region, picking up cold weather and sending it plunging southward, Harris said. He compared the effect to a skier picking up speed on a ski jump — the greater the speed one picks up, the farther the skier goes after leaving the jump.</p><p>The high pressure ridges usually occur two or more times during a la Nada period, he said. The first one came right on schedule this month, sending cold weather into the south-central U.S., including North Florida. It gave Little Rock, Ark., its first white Christmas since 1926.</p><p>But the second high pressure ridge, if it develops, tends to send cold weather even farther south — as much as 400 miles, Harris said. The only question is whether the next roller coaster points to Florida or farther west.</p><p>Harris put the odds of a citrus freeze reaching deeper into South Florida, including Polk County, at 40 percent. A citrus freeze occurs when temperatures reach 28 degrees or lower for at least four hours.</p><p>Florida has seen many minor freezes in the past two decades, but the last major freeze occurred on Christmas 1989 following other major freezes around Christmas 1983 and January 1985.</p><p>Some Wheeler Farms groves in Polk lost 80 percent of their trees during the 1989 freeze, Wheeler said.</p><p>Another variable hard to predict is whether temperatures will fall to 28 or lower for the required four hours, Harris said. Central Florida saw freezing weather for the first 14 days in January 2010, devastating tropical fish and tomato growers, but it mostly hovered above citrus freeze conditions.</p><p>Citrus growers may not be so lucky next month because temperatures in the far Northern Hemisphere have set record lows this winter, he said.</p><p>But even a mild freeze could cause major damage because of citrus greening, a fatal bacterial disease that weakens the tree. Scientists estimate the disease has infected more than half the state's citrus trees. </p><p>Florida growers are seeing record rates of premature fruit drop in the 2012-13 crop, which they attribute to the effects of greening.</p><p>Marty McKenna, a Lake Wales-based grower and chairman of the Florida Citrus Commission based in Bartow, said he doesn't sense any heightened concern among growers about a stronger chance of a freeze this season.</p><p>"If you make a statement there could be colder-than-normal temperatures in the middle of January, you'd be right most years," he said.</p><p>But McKenna did not play down the growers' concerns about the impact of a citrus on their already greening-stressed trees.</p><p>"With the introduction of greening, we've seen things we've never seen before," he said. "Who can say what will happen with this much greening? A freeze normally picks on weaker trees."</p><p>[ Kevin Bouffard can be reached at kevin.bouffard@theledger.com or at 863-401-6980. Read more on Florida citrus on his Facebook page, Florida Citrus Witness, http://bit.ly/baxWuU. ]</p>